Using a multiple cause definition of death, cause-specific mortality in American Somoa from 1900 to 1987 is examined to determine how and when different causes contributed to the transition from infections to degenerative diseases as the primary causes of death. The study design is unique in that several definitions of cause of death: total mentions, extended underlying cause, patterns, of failure and single underlying cause, are used to more clearly specify the differential contributions of various causes to total mortality over time. The 1900 to 1980 American Samoan mortality records provide an unusual opportunity to examine this transition in a presently developing population. Results from earlier research have shown that between 1950 and 1960 mortality from infections declined 71%, with an additional 15% decline occurring between 1960 and 1980. At the same time mortality from cardiovascular disease, cancer and other degenerative diseases, which accounted for 20% of all deaths in 1950, was responsible for an increasing proportion of total mortality, 43%, in 1980. This analysis is based on death certificates, recorded while the islands of American Somoa were a protectorate of the United States, and census data from the United States decennial censuses of outlying territories. The results should a) provide a clearer picture of health changes associated with mortality transitions in presently developing societies, b) identify those causes of death which are the most significant factors in mortality during the transition in a multiple- cause-of-death framework, c) inform policy makers in developing societies of disease influences and interactions on mortality during and following the transition which may not be obvious using a single underlying-cause-of-death model, and d) inform health planners in developed nations of the likely trends in mortality to be expected among their immigrant subpopulations from developing nations.